5^,7/r 


«*WB$‘TY  of  lLUNft’c 


r 


4 


[Reprinted  from  The  Journal  of  The  American  Chemical  Society, 
Vol.  XXVIII.  No.  3.  March,  1906.] 


[Contribution  from  the  Chemical  Laboratory  of  the  University 

of  Illinois.] 

ARSONIC  AND  ARSINIC  ACIDS. 

By  William  M.  Dehn  and  S.  J.  McGrath. 

Received  January  2,  1906. 

Arsonic  acids  may  be  considered  as  derived  from  arsenic  acid, 
AsO(OH)3,  by  replacing  one  of  the  hydroxyl  groups  by  a univalent 
hydrocarbon  or  substituted  hydrocarbon  radicle ; thus  the  arsonic 
acids  have  the  general  formula  R — AsO(OH)2.  Arsinic  acids 
may  be  considered  dialkyl  or  dialphyl  substitution -products  of 
arsenic  acid  and  have  the  general  formula  RR'AsOOH,  wherein  R 
and  R'  are  any  two  univalent  hydrocarbon  radicles.  All  of  the 
arsinic  acids  hitherto  prepared  have  the  two  radicles  identical, 
except  phenyl-/?-toluylcacodylic  acid.1  The  arsinic  acids  are,  of 
course,  homologues  of  cacodylic  acid  and  are  therefore  frequently 
termed  cacodylic  acids — for  instance  phenylarsinic  acid  is  also 
known  as  phenylcacodylic  acid. 

The  structural  formulas  usually  assigned  to  the  arsonic  and 
arsinic  acids  are: 

O— H R 

1 1 

R — As  = 0 and  R — As  = 0 

I I 

O— H O— H 

The  best  proof  of  the  direct  union2  of  the  radicles  with  arsenic 
is  seen  in  their  reduction  to  the  corresponding  arsines,3  which 
unquestionably  contain  the  radicles  in  direct  union  with  arsenic : 

RAs03H2  + 6H  = RAsH2  + 3H20 
R2AsOOH  + 4H  = R2AsH  + 2H20. 

The  possibility  here  of  molecular  rearrangement  is  precluded 

1 Ann.  321,  157. 

2 Ibid.  107,  269. 

3 Ber.  27,  1378;  Am.  Ch.  J.  33,  104. 


p.  15877 


C 


348 


WILLIAM  M.  DEHN  AND  S.  J.  MCGRATH. 


by  the  fact  that  the  arsines  spontaneously  reoxidize  to  the  re- 
spective acids  r1 

RAsH2  + 30=  RAsO  (OH)2 
R2AsH  + 20  = R2AsOOH. 

Proof  of  the  pentavalent  condition  of  the  arsenic  atoms  in  the 
arsonic  and  arsinic  acids  is  seen  in  their  stability  towards  oxidizing 
agents,  as  for  instance  toward  nitric  acid2  or  the  halogens. 3 Where- 
as all  soluble  arsenic  compounds  that  are  known  to  contain 
trivalent  arsenic  easily  reduce  nitric  acid  and  decolorize  bromine 
water,  the  arsonic  acids  and  the  arsinic  acids  are  indifferent  toward 
these  reagents,  therefore  their  arsenic  atoms  must  be  held  in  the 
pentavalent  condition. 

The  remainder  of  the  structure  of  the  arsonic  acids  and  the 
arsinic  acids  is  established  by  their  basicity.  The  arsonic  acids 
are  dibasic,4  and  the  arsinic  acids  are  monobasic;  the  former 
possess  two  hydroxyls  and  the  latter,  only  one.  All  of  the  facts 
are  therefore  in  accordance  with  the  above-mentioned  structural 
formulas. 

According  to  some  recent  work  of  Hantzsch,5  however,  con- 
ductivity measurements  of  methylarsinic  acid  (cacodylic  acid) 
tend  to  show  that  when  treated  with  an  excess  of  caustic  alkali, 
it  does  not  react  strictly  as  a monobasic  acid,  but,  at  least  in  part, 
as  the  sodium  salt  of  a tribasic  acid.  His  data  are  as  follows: 

(CH3)2As02Na+Na0H. 


(CH3)2As02Na. 

NaOH. 

By  addition. 

Found. 

Difference. 

56.8 

202.0 

258.0 

232.8 

25.2 

56.8 

201.9 

257+ 

233-1 

24.8 

Hantzsch  concluded  that  in  the  presence  of  one  molecule  of 
sodium  hydroxide,  cacodylic  acid  functionates  as  a monobasic 
acid, 

(CH3)2As02H  + NaOH  = (CH3)2As02Na  + H20, 
but  in  the  presence  of  an  excess  of  sodium  hydroxide  it  forms 
the  molecular  aggregate  (CH3)2As(OH)(ONa)2,  and  thus  cacodylic 
acid  functionates  also  in  the  tribasic  form  (CH3)2As(OH)3.  This 
effect  is  very  slight,  however,  and  disappears  entirely  in  N/48 
solution. 

1 Am.  Ch.  J.  33,  123;  35,  9. 

2 Ann.  46,  9;  Ibid.  208,  3,  32. 

3 Ibid.  201,  231. 

4 Ibid.  107,  290;  320,  277. 

5 Ber.  37,  1076.  . |f 


ARSONIC  AND  ARSINIC  ACIDS. 


349 


This  evidence  is  not  at  variance  with,  but  is  in  confirmation 
of,  the  above-mentioned  structural  formula,  that  is,  the  formula 
R R 

i i 

R — As  = O by  assimilation  of  water  becomes  R — As  = (OH)2, 

i ' i 

OH  OH 

the  former  bearing  to  the  latter  the  same  relation  that  meta- 
phosphoric  acid  does  to  orthophosphoric  acid. 

Methods  of  Preparation. — There  is  available  at  present  only 
one  good  general  method  for  the  preparation  of  both  arsonic  and 
arsinic  acids;  viz.,  the  hydrolysis  of  the  corresponding  radicle- 
halogen  compounds: 

RAsC14  + 3H20  = RAsO  (OH)2  + 4HC1 
R2AsC13  + 2H20  = R2AsOOH  + 3HC1. 

The  first  application  of  this  general  reaction  was  made  by 
Baeyer  in  the  preparation  of  cacodylic  acid:1 

(CH3)2AsC13  + 2H20  = (CH3)2AsOOH  + 3HCI. 

The  first  application  in  the  aromatic  series  was  made  by  La- 
Coste  and  Michaelis2  in  the  preparation  of  phenylarsonic  acid: 

C6H5AsC14  + 3H20  = C6H5AsO  (OH)2  + 4HCI. 

Modifications  of  the  above  general  method  are  found  in  the 
oxidation  of  monomethylarsine  dichloride  by  means  of  moist 
silver  oxide,3 

(CH3)  AsC12  + 2Ag20  + H20  = (CH3)  AsO(OH)2  + 2AgCl  + 2A  g ; 
the  oxidation  of  m-xylylarsine  dichloride  by  means  of  hydrogen 
peroxide,4 

(C8H9)  AsC12  + 2H202  = (C8H9)  AsO(OH)2  + 2HC1  + O ; 
and  the  oxidation  of  primary5  and  secondary6  arsines  by  atmos- 
pheric oxygen,  etc., 

RAsH2  + 30  = RAsO(OH)2, 

R2AsH  + 20  = R AsOOH. 

The  intermediate  compounds  in  the  preparation  of  arsonic 
and  arsinic  acids,  viz.,  the  trivalent  radicle-halogen  compounds, 
are  derived  by  two  general  reactions: 

1 Ann.  107,  268. 

2 Ibid.  201,  202. 

8 Ibid.  107,  268. 

4 Ibid.  320,  333. 

6 Ber.  34,  3594;  Am.  Ch.  J.  33,  124. 

6 Ber.  27,  1378;  Am.  Ch.  J.  35,  9. 


350 


WILLIAM  M.  DEHN  AND  S.  J.  MCGRATH. 


(1)  The  interaction  of  arsenic  trihalides  with  mercury  alkyl 
or  mercury  alphyl: 

HgR2  2 AsClg  = HgCl2  T 2RAsC12 
HgR2 + AsC13  = HgCl2  + R2AsC1. 

(2)  The  condensation  of  arsenic  trihalides  and  alkyl  or  alphyl 
monohalides  by  means  of  sodium: 

RC1  + AsC13  + 2Na  = RAsC12  + 2NaCl 
2RCI  + AsC13  + 4Na  = R2AsC1  + 4NaCl. 

The  first  application  of  reaction  (1)  to  the  aromatic  arsenic 
compounds  was  made  by  TaCos te  and  Michaelis1  in  the  prepara- 
tion of  phenylarsine  dichloride: 

(C6H5)2Hg  + 2AsC13  = 2 (C6H5)  AsC12  + HgCl2. 

The  first  in  the  fatty  series  was  made  by  LaCoste2  in  the  prep- 
aration of  ethylarsine  dichloride: 

(C2H5)2Hg  + 1 AsC13  = C2H5AsC12  + C2H5HgCl. 

The  first  application  of  reaction  (2)  to  the  aromatic  series  was 
made  by  Michaelis  and  Rees3  in  the  preparation  of  triphenyl- 
arsine  and  its  subsequent  transformation  to  phenylarsine  di- 
chloride on  heating  with  an  excess  of  arsenic  trichloride: 

3C6H5C1  + AsC13  + 6Na  = (C6H5)3As  + 6NaCl 
(C6H5)3As  + 2AsC13  = 3(C6H5)  AsC12. 

The  first  application  of  reaction  (2)  to  the  fatty  series  was  made 
by  Dehn  and  Wilcox4  in  the  preparation  of  mono-  and  diisoamyl- 
arsine  chlorides: 

C5HnCl  + AsC13  + 2Na  = C5HnAsCl2  + 2NaCl 
2C5HuC1 + AsC13  + 4Na  = (C5Hn)2AsCl  + 4NaCl. 

Besides  the  above  general  methods  for  the  preparation  of  arsonic 
and  arsinic  acids  there  are  a number  of  special  methods  which  are 
of  great  importance.  * 

(1)  The  reaction  of  alkyl  halides  with  alkali  arsenites  to  form 
fatty  arsonic  acids : 

As(ONa)3  + RI  = RAsO(ONa)2 + Nal. 

This  reaction  was  first  employed  by  Meyer,5  was  modified  by 
Klinger  and  Kreutz6  and  was  elaborated  and  extended  by  Dehn.7 

1 Ann.  201,  196. 

2 Ibid.  208,  33. 

3 Ber.  15,  2876. 

4 Am.  Ch.  J.  35,  48. 

5 Ber.  16,  1440. 

6 Ann.  249,  247. 

7 Am.  Ch.  J.  33,  131* 


ARSONIC  AND  ARSINIC  ACIDS. 


351 


(2)  The  preparation  of  cacodylic  oxide  by  heating  potassium 
acetate  and  arsenic  trioxide: 


4CH3CH2OK  + As203  = ((CH3)  2 As)20  + 2C02  + 2K2C03, 
and  its  oxidation  to  cacodylic  acid : 

((CH3)2As)20  + H20  + 2O  = 2 (CH3)2AsOOH. 

This  reaction  has  not,  however,  yielded  a single  homologue  of 
cacodylic  acid. 

The  arsonic  acids  hitherto  known  and  studied  are  as  follows: 


1.  Methyl.1 

2.  Ethyl.2 

3.  Phenyl.3 

4.  Nitrophenyl.4 

5.  Dimethylaminophenyl.1 

6.  /-Anisyl.6 

7.  /-Phenetyl.7 

8.  /-Benz.8 

9.  w-Benz.9 

10.  Nitrobenz.10 

11.  0-Toluyl.11 

12.  w-Toluyl.12 

13.  /-Toluyl.13 

14.  Nitrotoluyl.14 


15.  Tertiary  butylphenyl.15 

16.  0-Dimethylamino-/-tolyl.10 

17.  ra-Xylyl.16 

18.  /-X ylyl.17 

19.  Monochlorxylyl.18 

20.  Dichlorxylyl.18 

21.  Nitroxylyl.18 

22.  w-Tolu.19 

23.  /-Tolu.20 

24.  Phthalo.19 

25.  Pseudocumyl.21 

26.  /-Cumyl.21 

27.  a- naphthyl.22 

28.  /3-naphthyl. 23 


It  will  be  seen  that  though  some  twenty-six  arsonic  acids  of 
the  aromatic  series  have  been  prepared  only  two  of  the  fatty 
series  have  been  prepared.  We  herein  contribute  two  new  fatty 
arsonic  acids ; viz. : 


29.  Propyl. 


30.  Isoamyl. 


Also  the  aromatic  arsonic  acid, 

31.  Benzyl. 


The  arsinic  acids  hitherto  prepared  and  studied  are  the  follow- 
ing: 


1 Ber.  16,  1440;  Ann.  107,  263;  249,  149. 

2 Ann.  208,  34;  Am.  Ch.  J.  33,  132. 

3 Ibid.  201,  203. 

4 Ber.  27,  265. 

6 Ann.  270,  139. 

8 Ber.  20,  51. 

7 Ann.  320,  300. 

8 Ibid.  208,  5. 

Ibid.  320,  329. 

10  Ibid.  320,  325. 

11  Ibid.  201,  255. 

12  Ibid.  320,  328. 


13  Ibid.  201,  255. 

14  Ibid.  320,  321. 
16  Ibid.  320,  342. 

16  Ibid.  320,  333. 

17  Ibid.  320,  338. 

18  Ibid.  320,  334. 

19  Ibid.  320,  335. 

20  Ibid.  320,  339. 

21  Ibid.  320,  340. 

22  Ber.  11,  1503. 

23  Ann.  320,  344. 


352 


WILLIAM  M.  DEHN  AND  S.  J.  MCGRATH. 


1.  Methyl.1  4.  Benzyl.4  7.  Benz.7 

2.  Ethyl.2  5.  />-Toluyl.5  8.  Phenyl-^-toluyl.8 

3.  Phenyl.3  6.  Nitrophenyl.6  9.  Isoamyl.9 

Normal  Propylarsonic  Acid. — This  acid  was  prepared  in  the 

same  manner  as  ethylarsonic  acid.10  To  275  grams  of 
arsenic  trioxide  (1  mol.)  and  460  grams  of  potassium  hydroxide 
(6  mols.),  sufficient  water  was  added  to  cause  complete  solution. 
After  cooling,  alcohol  was  added  to  the  point  of  incipient  pre- 
cipitation of  potassium  arsenite ; then  460  grams  of  normal  propyl 
iodide  (2  mols.)  were  added  and  the  mixture  was  shaken.  Usually 
either  some  potassium  arsenite  or  some  propyl  iodide  precipitates 
at  this  stage,  but  a homogeneous  solution  may  be  produced  by 
adding  either  water  or  alcohol;  or,  when  the  solution  is  too  con- 
centrated, both  must  be  added.  After  keeping  the  mixture  in 
tightly-stoppered  bottles  for  a number  of  days,  the  following 
reaction : 

As  (OK)  3 + C3H7I  = (C3H7)  AsO(OK)2  + KI, 
and  the  unavoidable  side-reaction: 

C2H5OK  + C3H7I  = C2H5— 0— C3H7  + KI, 
were  complete.  The  mixture  was  then  subjected  to  distillation, 
to  remove  the  alcohol  and  the  ethylpropyl  ether.  Hydrochloric 
acid  was  added  to  the  point  of  incipient  precipitation;  then  a 
stream  of  chlorine  was  passed  in  until  the  pure  white  double 
salt11  first  formed  was  dissolved  and  all  of  the  iodine  was  pre- 
cipitated. The  filtrate  was  treated  in  the  cold  with  magnesium 
mixture  to  precipitate  the  arsenate ; upon  boiling  the  filtrate  from 
the  ammonium  magnesium  arsenate,  with  more  magnesium  mix- 
ture, the  magnesium  salt  of  normal  propylarsonic  acid  was  pre- 
cipitated as  pearly-white,  soapy  crystals.  Yield,  42  per  cent.  The 


magnesium  salt  was  dried  and  analyzed : 

Per  cent.  Mg. 

Salt  dried  at  ioo°-io5°  for  eight  hours 11.93 

Salt  dried  at  i30°-i4o°  for  six  hours 11 .99 

Salt  dried  at  I35°-i6o°  for  four  hours 12.09 

Salt  dried  at  I90°-2oo°  for  five  hours *3-38 

Theory  for  (C3H7As03Mg)2H20 12.05 

Theory  for  C3H7As03Mg 12.48 

1 Ann.  46,  2.  7 Ibid.  321,  151. 

2 Ibid.  92,  365.  8 Ibid.  321,  157. 

3 Ibid.  201,  231;  321,  150.  9 Am.  Ch.  J.  35,  52. 

4 Ibid.  233,  82.  10  Ibid.  33,  132. 

6 Ibid.  208,  20.  11  Ibid.  33,  141. 

6 Ibid.  208,  25. 


ARSONIC  AND  ARSINIC  ACIDS. 


353 


These  analyses  indicate  that  the  magnesium  propylarsonate, 
like  magnesium  ammonium  arsenate1  dried  above  ioo°,  contains 
one  molecule  of  water  of  crystallization  to  two  molecules  of  the 
anhydrous  salt.  Drying  above  190°  not  only  removed  this 
water  of  crystallization  from  magnesium  propylarsonate  but  also 
partially  decomposed  the  salt.  Its  probable  structural  formula 
is: 

OH 

1 

C3H7 — As  = 02Mg 

I 

0 

1 

C3H7— As  = 02Mg 

OH 

Free  n-propylarsonic  acid  was  prepared  by  treating  the  mag- 
nesium salt  in  the  cold  with  the  calculated  quantity  of  concen- 
trated sulphuric  acid  and  then  extracting  with  alcohol.  Upon 
evaporating  the  alcoholic  solution  the  acid  was  obtained  as 
needle-form  crystals. 

The  acid  is  very  soluble  in  water;  100  parts  of  an  aqueous  solu- 
tion at  26°  contained  43  parts  of  acid.  It  is  also  very  soluble 
in  alcohol  but  is  insoluble  in  ether. 

u^Propylarsine  Disulphide. — A quantity  of  the  magnesium 
propylarsonate  was  dissolved  in  dilute  hydrochloric  acid  and 
treated  with  hydrogen  sulphide.  A heavy,  light  yellow  oil  was 
slowly  precipitated.  It  was  extracted  with  carbon  bisulphide, 
dried  with  calcium  chloride  and  freed  from  the  solvent  by  evapora- 
tion. The  analysis  gave  35.29  per  cent,  of  S.  Calculated  for 
C3H7AsS2,  35.16  per  cent. 

Therefore  the  reaction  was: 

C3H7AsO(OH)2  + 2H2S  = C3H7AsS2  + 3H20. 

The  density  of  the  disulphide  was  found  to  be  1.8.  It  is  a 
viscid  oil  that  becomes  a gummy  mass  below  — io°. 

Isoamylarsonic  Acid. — This  acid  was  prepared  in  a manner 
nearly  identical  with  the  manner  of  preparation  of  the  w-propyl- 
arsonic  acid.  One  molecule  of  arsenic  trioxide  (150  grams)  was 
dissolved  in  six  molecules  of  potassium  hydroxide  (254  grams) 
and  treated  with  two  molecules  of  isoamyl  iodide  (300  grams). 

1 Z.  anal.  Chem.  10,  62. 


354 


WILLIAM  M.  DEHN  AND  S.  J.  MCGRATH. 


The  reaction  mixture  was  permitted  to  stand  for  two  or  three 
days,  when  the  alcohol  was  removed  by  distillation;  the  solution 
was  then  carefully  neutralized  and  filtered  from  the  double  salt  of 
As203.2KI.  Upon  acidifying,  a mass  of  shining  scale-like  crystals 
separated,  usually  after  some  time;  they  were  filtered  off,  washed, 
recrystallized,  dried  and  analyzed.  Calculated  for  C5HnAsO(OH)2 : 
C,  30.61;  H,  6.84.  Found:  C,  30.21;  H,  6.63. 

The  magnesium  salt  was  easily  prepared  by  boiling  the  acid 
with  magnesium  mixture.  Isoamylarsonic  acid  is  a pearly  white 
crystalline  substance  that  melts  at  1940 ; 100  cc.  of  a saturated 
aqueous  solution  at  28°  contains  0.820  gram;  an  equal  quantity 
of  a saturated  alcoholic  solution  at  210  contains  2.2  grams.  Like 
the  other  arsonic  acids  it  is  insoluble  in  ether. 

Isoamylarsine  Disulphide. — This  sulphide  was  prepared  as 
was  the  normal  propyl  disulphide.  It  is  a viscid,  light-yellow 
oil  that  will  not  solidify  in  a freezing-mixture  and  cannot  be 
distilled  without  decomposition.  The  analysis  gave  30.62  per 
cent,  of  S.  Calculated  for  C5HnAsS2,  30.48  per  cent. 

Benzylarsonic  Acid. — Of  all  the  arsonic  acids,  this  is  the 
most  easily  prepared.  When  quantities  of  the  substances  in- 
dicated by  the  equation, 

2C6H5CH2I  + As203  + 6KOH  = 2C6H5CH2AsO  (OK)2  + 2KI  + 3H20, 
are  dissolved  in  a mixture  of  alcohol  and  water  in  the  manner 
previously  described,  freed  from  the  alcohol  by  distillation,  first 
neutralized  and  then  carefully  acidified  with  hydrochloric  acid, 
a precipitation  of  benzylarsonic  acid  to  the  extent  of  60  per  cent, 
occurs. 

Benzylethyl  ether,  equal  to  the  loss  of  benzyl  iodide  not  fixed 
by  the  arsenite,  may  be  recovered  from  the  alcohol  removed  by 
distillation1.  Upon  washing  the  free  acid  with  water  and  re- 
crystallizing once  from  water  or  alcohol  it  is  easily  obtained 
pure.  The  analysis  gave:  C,  38.65;  H,  4.20.  Calculated  for 
C6H5CH2AsO(OH)2 : C,  38.88;  H,  4.16. 

Benzylarsonic  acid  crystallizes  in  long,  beautiful,  white, 
glistening  needles.  It  melts  at  167°.  It  dissolves  with  difficulty 
in  cold  water  but  is  quite  easily  soluble  in  hot  water;  100  cc.  of 
a saturated  aqueous  solution  at  22.50  contains  0.34  gram;  at 
27°,  0.39  gram;  and  at  970  contains  3.50  grams  of  the  acid.  Its 
solubility  in  alcohol  is  indicated  by  the  following  data:  100  cc. 

1 Am.  Ch.  J.  33,  142. 


ARSONIC  AND  ARSINIC  ACIDS. 


355 


of  a saturated  alcoholic  solution  at  23°  contains  0.87  gram  of  acid 
and  at  70°,  5.91  grams  of  the  acid.  It  is  stable  in  the  air,  has  no 
odor  but  has  a peculiar  bitter  taste.  It  has  an  irritating  effect 
upon  the  epidermis  and  the  mucous  membrane.  An  aqueous 
solution  of  the  acid  gives  with  silver  nitrate  a white  precipitate 
of  the  silver  salt,  and  with  magnesium  mixture  on  boiling,  a 
white  precipitate  of  the  magnesium  salt. 

Benzylarsine  Disulphide. — Treated  with  hydrogen  sulphide 
benzylarsonic  acid  slowly  precipitates  the  benzylarsine  disulphide, 
C6H5CH2AsS2,  which  is  very  similar  in  properties  to  the  arsine 
disulphides  previously  described.  It  is  a heavy,  bright-yellow 
oil  that  dissolves  rapidly  in  nitric  acid,  liberating  sulphur  and 
oxides  of  nitrogen.  On  being  heated  alone  it  gives  off  hydrogen 
sulphide  and  forms  arsenic  trioxide  and  stilbene.  The  reaction 
is,  probably: 

2C6H5CH2AsS2  = C6H5CH=CHC6H5 + As203  + H2S. 

Decomposition  of  Benzylarsonic  Acid  by  Heat. — Benzylarsonic 
acid  on  being  heated  yields  the  following  decomposition  products : 
Benzyl  alcohol,  benzaldehyde,  stilbene,  water  and  arsenic  trioxide. 
Probably  the  most  important  reaction  is: 

2C6H5CH2AsO(OH)2  = C6H5CH2OH  + C6H5CHO  + As203  + 3H20, 
while  stilbene  is  formed  in  smaller  quantities  according  to  the 
equation : 

2C6H5CH2AsO(OH)2  = C6H5CH=CHC6H5  + As203  + 3H20. 

Upon  heating  the  corresponding  arsinic  acid,  (C6H5CH2)2AsOOH, 
Michaelis  and  Paetow1  found  that  it  decomposed  according  to 
the  following  reaction : 

2 (C6H5CH2)2AsOOH  = As2  + 2H20  + 2C6H5CHO  + (C6H5CH2)2. 

When  50  grams  of  benzylarsonic  acid,  containing  some  water 
of  crystallization,  were  heated  in  a small  flask  attached  to  a 
condenser,  an  emulsion  having  the  odor  of  benzaldehyde  passed 
over.  On  standing,  15  grams  of  water  separated.  The  oil  was 
shaken  with  a concentrated  aqueous  solution  of  sodium  bisul- 
phite until  the  odor  of  benzaldehyde  was  discharged,  and  was 
then  extracted  with  ether.  On  acidifying  and  distilling  with 
steam,  the  aqueous  solution  was  easily  proved  to  contain  benzal- 
dehyde. The  ether  solution,  after  drying  with  calcium  chloride, 
was  distilled  and  gave  a fraction  which  boiled  largely  between 
200°  and  210°  (benzyl  alcohol  boils  at  206°).  This  fraction  was 
1 Ann.  233,  83. 


356 


WIUvIAM  M.  DEHN  AND  S.  J.  MCGRATH. 


treated  with  acetyl  chloride  and  benzoyl  chloride  and  yielded 
benzyl  acetate  (io6°)  and  benzyl  benzoate  (3290)  respectively. 
The  quantities  of  benzyl  alcohol  and  benzaldehyde  produced  were 
approximately  equal ; therefore,  the  following  reaction  is  es- 
tablished : 

2C6H5CH2AsO  (0H)2 = C6H5CH2OH  + C6H5CHO + As203  + H20. 

A higher  fraction  boiling  between  300°  and  310°  was  obtained, 
(stilbene  boils  at  306°  and  dibenzyl  boils  at  284°).  It  was,  how- 
ever, too  small  in  quantity  to  be  purified  by  fractionation  and  it 
could  not  be  crystallized  by  cooling  in  a freezing-mixture.  A 
combustion  gave: 

Calculated  for  Calculated  for  Calculated  for 
Substance.  stilbene.  dibenzyl.  benzyl  alcohol. 

C 84.65  93.34  92.30  77.07 

H 7.95  6.66  7.70  7.64 

Evidently  the  higher  fraction  was  a mixture  of  benzyl  alcohol 
and  stilbene  rather  than  benzyl  alcohol  and  dibenzyl.  Further 
evidence  for  this  conclusion  is  seen  in  its  easy  decolorization  of 
bromine  water.  Therefore  it  may  safely  be  held  that  a secondary 
decomposition  of  benzylarsonic  acid  by  means  of  heat  is  : 
2C6H5CH2As(OH)2  = C6H5CH=CHC6H5+As203  + 3H20. 

Decomposition  of  Benzylarsonic  Acid  by  Acids. — Unlike  its 
homologues  and  isologues,  benzylarsonic  acid  is  easily  decom- 
posed by  mineral  acids.  Michaelis  and  Paetow1  observed  that 
concentrated  hydrochloric  acid  completely  decomposed  dibenzyl- 
arsonic  acid  into  arsenic  trichloride,  benzyl  chloride  and  toluene, 
according  to  the  equation : 

(C6H5CH2)2AsOOH  + 4HCI = C6H5CH2C1  + C6H5CH3 + AsC13  + 2H20. 

With  concentrated  hydrochloric  acid  we  find  that  benzylarsonic 
acid  is  decomposed  into  benzyl  chloride  and  arsenious  acid  (no 
toluene  was  detected),  therefore  the  reaction  is: 

2C6H5CH2AsO(OH)2  + 2HC1  = 2C6H5CH2C1  + As203  + 3H20. 

With  sulphuric  acid  we  find  that  dibenzyl,  benzaldehyde,  and 
arsenious  acid  are  the  decomposition-products,  therefore,  the 
following  reaction  is  probable: 

4C6H5CH2AsO(OH)2  = (C6H5CH2)2  + 2C6H5CHO  + 2As203  + 4H20. 

The  speed  of  the  above  reaction  may  be  determined  by  titration 
with  a standard  iodine  solution,  free  iodine  having  no  effect  on 
1 Ann.  233,  84. 


ARSONIC  AND  ARSINIC  ACIDS. 


357 


arsonic  acids.  The  accompanying  table  shows  the  great  speed 
of  the  decomposition: 


Weight  of  benzyl- 
arsonic  acid. 

h2o. 

cc. 

h2so4. 

cc. 

Time. 

Minutes. 

Temperature. 

Decomposition. 
Per  cent. 

I.5°° 

25 

IO 

30 

IOO° 

IOO 

I.500 

25 

IO 

15 

100 

IOO 

I.318 

25 

5 

5 

IOO 

99 

I.318 

25 

5 , 

5 

loo 

99-4 

1. 172 

25 

1 

10 

IOO 

92 

The  decomposition  with  sulphuric  was  much  more  rapid  than 
with  hydrochloric  acid.  When  phenyl-  and  ethylarsonic  acids 
were  treated  in  the  same  manner  only  traces  of  arsenious  acid 
were  detected. 

Decomposition  of  the  Salts  of  Fatty  Arsonic  Acids  by  Heat. — It 
was  found  by  Dehn1  that  heat  decomposed  magnesium  ethyl- 
arsonate  into  magnesium  oxide,  metallic  arsenic,  water  and  a 
hydrocarbon  gas. 

A closer  study  of  this  decomposition  was  made  by  us  and  it 
was  found  that  the  hydrocarbon  gas  given  off  is  a mixture  of 
methane  and  ethylene.  The  unsaturated  gas  was  separated 
from  the  methane  by  treatment  with  bromine  water,  and  the 
ratio  of  their  volumes  was  found  in  one  case  to  be  42.5  per  cent, 
of  the  former  to  57.5  per  cent,  of  the  latter.  A combustion"  of 
the  residual  gas  gave  the  following  data: 

43.5  cc.  of  gas  (corrected  and  equal  to  0.0317  gram)  gave  0.0863 
gram  of  C02  and  0.0714  gram  of  H20. 

Calculated  for  CH4.  Found. 


Carbon 75- 00  75. 10 

Hydrogen 25.00  24.04 


An  analysis  of  the  saturated  gas  by  the  explosion  method  gave 
the  following  results: 


Vol.  gas 
saturated. 

Vol.  C02 
theory. 

Vol.  C02 
found. 

Vol.  H20 
theory. 

Vol.  HoO 
found. 

I. 

10.2 

10.2 

10.4 

20.4 

20.4 

II. 

12.0 

12.0 

1 1. 8 

24.O 

24.2 

Evidently,  the  saturated  gas  is  methane. 

An  analysis  of  the  mixture  of  saturated  (57.5  per  cent.)  and 
unsaturated  (42.5  per  cent.)  gases  was  made  by  the  explosion 
method  and  gave  the  following  data: 

1 Am.  Ch.  J.  33,  133. 


358 

WILLIAM  M.  DLHN  AND  S.  J.  MCGRATH. 

Volume  gas 
saturated  and 
unsaturated. 

Volume  COa 
calculated. 

Volume  C02 
found. 

Volume  H20 
calculated. 

Volume  H20 
found. 

I. 

8.4 

12.0 

11. 8 

16.8 

16.6 

2. 

9.0 

12.0 

12.8 

18.O 

18.2 

This  indicates  that  the  unsaturated  gas  is  ethylene.  An 
equation  proposed  to  represent  the  decomposition  of  magnesium 
ethylarsonate  is  as  follows: 

(C2H5As03Mg)2H20  = 2CH4  + C2H4  + Mg2As207. 

This,  however,  cannot  represent  the  entire  reaction,  for  water 
is  formed  as  well  as  a larger  quantity  of  ethylene  than  is  indicated 
by  the  equation.  As  magnesium  ethylarsonate  is  dehydrated 
and  partially  decomposed  at  145-1700,1  the  following  secondary 
reaction  may  occur: 

2C2H5As03Mg  = C2H4  + H20  + Mg2As205. 

Furthermore  as  carbon  dioxide  (10-18  per  cent,  of  the  evolved 
gases)  and  metallic  arsenic  are  found  among  the  end-products, 
other  reactions  are  probably  necessary  to  represent  the  complete 
decomposition. 

Decomposition  of  Magnesium  n-Propylarsonate  by  Heat. — 
When  magnesium  n-propylarsonate  was  heated  in  an  apparatus 
filled  with  carbon  dioxide,  it  yielded  a gaseous  product  which, 
when  freed  from  carbon  dioxide,  was  soluble  in  bromine  water 
to  the  extent  of  40  per  cent. ; therefore  this  gaseous  product  con- 
sisted of  40  per  cent,  of  an  unsaturated  hydrocarbon  and  60  per 
cent,  of  a residual  gas  whose  analysis  indicated  a mixture  of 
hydrogen  with  methane.  In  the  analysis  given  below,  the  gas  in 
experiment  (a)  was  obtained  from  the  total  evolved  gas,  while 
in  experiment  ( b ) the  gas  was  obtained  from  that  last  evolved 
during  the  heating  of  the  arsonate. 


(«) 

Volume 

gas. 

Volume  C02 
found. 

Volume  HsO 
found. 

Volume  HsO 
calc,  for  Ho. 

Volume  H20 
calc,  for  CH4. 

Volume  C02 
calc,  for  CH4. 

I. 

15.O 

8.6 

254 

15.0 

30.0 

15.0 

2. 

II-5 

6.2 

18.6 

1 1-5 

23.O 

11. 5 

3- 

12.0 

6.9 

19.8 

12.0 

24.O 

12.0 

This  experiment  shows  that 

the  saturated  gas 

consists  of 

nearly  equal  parts  of  hydrogen  and  methane. 

(*) 

Volume 

gas. 

Volume  C02 
found. 

Volume  HsO 
found. 

Volume  H20 
calc,  for  H2. 

Volume  H20 
calc,  for  CH4. 

Volume  C02 
calc,  for  CH4. 

1. 

10.8 

'7.3 

14. 1 

10.8 

21.6 

10.8 

2. 

10.2 

7.0 

13-2 

10.2 

20.4 

10.2 

3- 

IO.7 

7-3 

13-7 

IO.7 

21.4 

10.7 

Am.  Ch.  J.  33,  133. 

ARSONIC  AND  ARSINIC  ACIDS. 


359 


This  experiment  shows  about  70  per  cent,  of  methane  and  30 
per  cent,  of  hydrogen. 

When  40  grams  of  magnesium  w-propylarsonate  were  heated 
so  that  the  gaseous  products  were  passed  through  bromine  water, 
a quantity  of  halogen-olefine  addition-product  was  obtained. 
Distillation  of  the  oil  yielded  fractions  that  boiled  near  the  boiling- 
points  of  ethylene  bromide  (129.50)  and  propylene  bromide 

(hi0)- 

Analysis  of  the  first  fraction  by  the  Carius  method  gave  85.35 
per  cent.  Br;  calculated  for  C2H4Br2,  85.11  per  cent. 

The  second  fraction  gave  78.42  per  cent.  Br;  calculated  for 
C2H5BrCH2Br,  79.71  per  cent. 

The  above  experiments  prove  the  presence  of  hydrogen, 
methane,  ethylene,  and  propylene.  However,  at  present,  the 
evidence  on  the  decomposition  of  magnesium  w-propylarsonate 
is  too  slight  to  venture  writing  the  equations  involved. 

Meyer's  Reaction. — The  above-described  arsonic  acids  were 
prepared  by  Meyer’s  reaction,  that  is,  by  application  of  the  follow- 
ing general  reaction: 

R X + K3As03  = K2RAs03  + KX. 

Evidence  for  their  formation  was  obtained  in  preliminary 
experiments1  by  determination  of  the  per  cent,  of  transformation 
of  arsenite.  Other  preliminary  studies  along  this  line  are  given 
below. 


Haloid  derivative. 

Time. 

Hours. 

Temperature. 

Yield. 
Per  cent. 

Isobutyl  iodide 

25° 

5 

cc  cc 

4 

25 

9 

CC  cc 

32 

25 

IO 

“ “ 

25 

IO 

cc  cc 

0-5 

80 

12 

1 c cc 

3 

80 

12 

Chloroform 

I 

25 

I 

“ 

4 

25 

1 

“ 

45 

25 

4 

“ 

98 

25 

4.8 

Bromoform 

1 

25 

5 

“ 

42 

25 

15 

“ 

53 

25 

23 

“ 

96 

25 

30 

“ 

25 

30 

Am.  Ch.  J.  33,  138- 


360 


ARSONIC  AND  ARSINIC  ACIDS. 


Haloid  derivative 

Time. 

Hours. 

Temperature. 

Yield. 

Per  cent. 

Iodoform  

23 

35-4. 

44 

4o 

23 

50 

5i 

23 

52.9 

4 < 

94 

23 

79 

4 4 

1 14 

23 

81.5 

4 4 

23 

92.2 

4 4 

0.5 

80 

50 

4 4 

80 

51 

4 4 

2.5 

80 

54 

4 l 

15 

80 

86 

/-Chlortoluene 

i 

25 

0 

“ 

42 

25 

3 

“ 

96 

25 

3 

Allyl  iodide  

25 

39 

“ “ 

0.5 

25 

45 

“ “ 

1 

25 

46 

“ “ 

25 

5i 

These  determinations 

were  made  by  titrating  the  unchanged 

potassium  arsenite  with  standard  solutions  of  iodine,  and  thus 
determining  by  difference  the  quantity  which  had  been  trans- 
formed into  the  arsonic  acid.  The  allyl  iodide  appeared  to  act 
abnormally,  first  a brown  precipitate  being  formed,  and  then  a 
yellow  oil. 

Jit  is  evident  from  these  experiments  that  other  arsonic  acids 
besides  those  hitherto  described  may  easily  be  prepared. 

Properties  of  the  Arsonic  and  Arsinic  Acids. — All  of  these  acids 
are  beautiful  white  crystalline  substances  which  are  usually  quite 
easily  soluble  in  water  and  alcohol  and  are  almost  insoluble  in 
ether. 

Solubilities  and  melting-points  as  determined  by  us  are  given 
in  the  accompanying  table: 


Acid. 

Solvent. 

Temperature. 

Soluble  in  100 
parts. 

Melting- 

point. 

Ethylarsonic. 

Water. 

270 

70.00 

99-5° 

4 4 4 4 

“ 

40 

112.00 

“ “ 

Alcohol.1 

25 

3940 

Propylarsonic. 

Water. 

26 

43.00 

125.0 

Isoamylarsonic. 

“ 

28 

0.82 

194.0 

“ “ 

Alcohol. 

21 

2.20 

Benzylarsonic. 

“ 

23 

O.87 

167.0 

4 4 4 4 

“ 

70 

5.91 

“ “ 

Water. 

22.5 

0-34 

1 The  alcohol  used 

in  these  experiments  was 

of  95  per  cent. 

concentra- 

tion. 


ARSONIC  AND  ARSINIC  ACIDS. 


361 


Acid. 

Solvent. 

Temperature. 

Soluble  in  100 
parts. 

Melting- 

point. 

Benzylarsonic. 

Water. 

27 

o-39 

“ “ 

“ 

97 

3-50 

Phetiylarsonic. 

“ 

28 

3- 25 

I58.O 

“ “ 

“ 

4i 

4.82 

“ 

52 

8.52 

“ 

84 

24.00 

Alcohol. 

26 

15-51 

“ “ 

“ 

68 

55-40 

Methylarsinic. 

Water. 

22 

82.90 

Phenylarsinic. 

“ 

27 

0.28 

164.O 

“ “ 

Alcohol. 

22 

11.80 

“ “ 

“ 

55 

57-7° 

Urbana,  III.,  December  27,  1905. 


